The present invention relates to vehicle drag reduction for improved fuel economy, and more particularly to streamlining of long-haul freight vehicles such as truck-tractor trailer rigs.
The boxy shape of conventional tractor-trailer combinations is dictated by a need to provide a large cargo volume within the maximum allowable dimensions that are fixed by state laws. In the past, the low aerodynamic efficiency of these vehicles was considered of little importance. However, the high cost and uncertain availability of fossil fuels has increasingly focused attention on reducing the aerodynamic drag that accounts for approximately half of the fuel consumption of large trucks in long-haul highway operations.
The potential economic benefit of drag-reduction apparatus can be evaluated based on the fuel that would be saved using the apparatus, the saving being independent of vehicle weight and rolling resistance. For example, a conventional tractor-trailer combination weighing about 25,000 pounds and having a cross-sectional area of 100 square feet and a drag coefficient of 1.0 typically consumes about 20 gallons of diesel fuel per hundred miles at 55 MPH, the fuel costing $16 at a price of $0.80 per gallon. The truck requires about 165 horsepower to overcome about 350 pounds of rolling drag and about 775 pounds of aerodynamic drag. A ten percent reduction in the aerodynamic drag results in a savings of ##EQU1## This is equivalent to a savings of about 1.33 gallons or $1.06 per hundred miles, independent of vehicle loading. On a trip of 2,000 miles, the savings is more than $21.
At higher speeds, air drag is greater and there is a corresponding greater reduction in drag for even greater savings. For example, on a 2,000 mile trip at 65 MPH, the aerodynamic drag increases 40% and a ten percent reduction results in a savings of about $30 in fuel costs. The potential savings are $60 per 2000 miles at 65 MPH with a 20% reduction in drag. Further, when the effects of wind are considered, the potential savings are even greater. Moreover, the cost and availability of diesel fuel are subject to change, potentially making aerodynamic drag a critical factor in shipping economy.
Although there are a variety of devices in the prior art for improving the aerodynamics of truck vehicles, these devices exhibit at least some of the following disadvantages:
1. they are ineffective in that they provide little or no drag reduction in actual use;
2. they are awkward to use in that they interfere with normal loading and maintenance operations;
3. they are heavy and bulky, being difficult to install, remove, and store when not in use;
4. they are unsafe in that they interfere with lighting visibility;
5. when permanently installed on a tractor, they increase the drag of dead-heading without a trailer; and
6. they are costly to produce and install.
Thus there is a need for streamlining apparatus for trucks that is effective for significantly reducing fuel consumption, is safe and easy to use and inexpensive to produce and install.